The following information is provided to assist the reader in understanding technologies disclosed below and the environment in which such technologies may typically be used. The terms used herein are not intended to be limited to any particular narrow interpretation unless clearly stated otherwise in this document. References set forth herein may facilitate understanding of the technologies or the background thereof. The disclosure of all references cited herein are incorporated by reference.
Determination of aqueous nitrate concentration is important for a variety of public and commercial applications. Nitrate is a common contaminate in water, and high quantities of nitrates in drinking water can be harmful to people and animals. Thus, there is a need to carefully monitor nitrate levels in water. Limits on acceptable nitrate concentration have been established for drinking water. Nitrate concentrations may, for example, be monitored in drinking water supplies, sewage, waste water, water remediation, biological samples, sea water, etc.
Methodologies for measuring aqueous nitrate concentration include spectrophotometry, colorimetry, chromatography, ion selective electrodes, etc. Various shortcomings exist with these methods including toxicity of reagents, cost, sensitivity, selectivity, variability, range, stability, time requirements, portability, etc.
In a number of colorimetric nitrate tests, nitrate is first reduced to nitrite, followed by nitrite analysis. Typically, reduction of nitrate to nitrite is accomplished using cadmium. Then, nitrite concentration is determined using the Griess assay or test. Nitrate concentration is directly related to nitrite concentration. However, cadmium may be toxic and is likely to be prohibited for use in water testing. Moreover, shaking is required in cadmium-containing systems, which may affect the surface reaction that occurs in the use of cadmium to reduce nitrate to nitrite, resulting in variability in testing. Zinc has also been used as a reductant in the nitrate test, but Zn is not as selective as Cd and can result in over-reduction of the nitrate to NO.
Portable water testing equipment such as the PORTABLE PARALLEL ANALYZER™ (available from Hach Company of Loveland, Colo.) has been introduced in which the test reagents are deposited (dried) upon a test element (for example, the CHEMKEY® test element available from Hach Company) that can be easily inserted into the equipment and utilized in field testing. The nature of the test elements and associated equipment limit or prevent the use of solid reagents. In that regard, water soluble reagents of an analysis system are dried upon the test element. Insoluble solids are difficult to deposit on test elements/chips. Solid reagents in nitrate testing, such as cadmium and zinc, cannot be used in such testing equipment.
The sulfoxidation of thioethers with nitrate as the oxidant and a homogeneous Mo/Cu(II) co-catalyst system has been reported as a pathway to sulfoxides in organic solvent such as acetonitrile. A variety of thioethers were shown to undergo the reaction to a greater or lesser extent. Organic-soluble thioether reagents and catalysts were also shown to be suitable for detection of nitrates in certain environments.